The carcinogens, 3,4-benzo(a)pyrene (BP) in ferric oxide, or N- methyl-N-nitrosourea (NMU) were injected into the submucosa of the same endobronchial site at weekly intervals in 5 sets of mongrel dogs. Weekly bronchoscopic photographs were used to record gross changes, and monthly changes, and monthly punch biopsies were taken from the sites of carcinogen application. The first set of dogs had 18 injections each of 90 mg BP-ferric oxide. The second group had up to 24 injections each of 15-45 mg NMU, and this schedule proved to be excessively toxic. In the third set of dogs, BP-ferric oxide injections were given until localized squamous metaplasia was induced. Thereafter, weekly topical applications of NMU were initiated and these are continuing. The last 2 groups are inbred beagles injected with BP; half of those are being treated with immunosuppressives. Dogs injected with BP-ferric oxide alone have been followed up to 52 weeks, and they have had up to 12 biopsies at the site of carcinogen injections. The dogs which had NMU injections have had up to 11 monthly biopsies. Up to 8 monthly biopsies have so far been obtained from dogs treated sequentially with endobronchial injections of BP and topical applications of NMU. Edema, bronchostenosis and mucosal irregularities, grossly consistent with neoplasia as it appears bronchoscopically in humans, was repeatedly observed in all groups to varying degrees. Columnar hyperplasia and/or squamous metaplasia are currently consistent findings in all groups. Bronchogenic carcinoma has not been observed to date, but 8 dogs have developed marked squamous atypia as a result of the carcinogens. We conclude that direct recurrent transbronchoscopic submucosal injections of carcinogens is feasible and practical in dogs. Both BP and NMU effectively induce localized squamous metaplasia, and a canine lung cancer model may be in the making.